(R)-3-hexyl-5,6-dihydro-4-hydroxy-6-undecyl-2H-pyran-2-one and (R)-5,6-dihydro-6-undecyl-2H-pyran-2,4(3H)-dione are known precursors for the preparation of tetrahydrolipstatin, which exist in tautomeric form.
The known methods of preparing (R)-3-hexyl-5,6-dihydro-4-hydroxy-6-undecyl-2H-pyran-2-one, include that set forth in Barbier, et al., J. Org. Chem., Vol. 53, pgs. 1218-1221 (1988). In particular, that process comprises a multiple step process described in reaction scheme I below: ##STR5## (a) Octanoic acid, LDA; (b) H.sub.2, Pd/C, 10%; (c) p-TsOH, CHCl.sub.3 ; (d) Jones' oxidation;
A method for the preparation of (R)-5,6-dihydro-6-undecyl-2H-pyran-2,4(3H)-dione includes that set forth in co-pending U.S. application Ser. No. 07/653,846, filed Feb. 11, 1991. In particular, that process comprises hydrogenolyzing and cyclizing a compound of the formula: ##STR6## wherein R.sup.2 is C.sub.11 H.sub.23 ; Ar is phenyl substituted by 1 to 3 groups R.sup.9 or OR.sup.9 wherein R.sup.9 is hydrogen or C.sub.1-3 alkyl.